/*-------------------------------------------------------------------------
 *
 * keys.c--
 *    Key manipulation routines
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /usr/local/cvsroot/postgres95/src/backend/optimizer/util/keys.c,v 1.1.1.1 1996/07/09 06:21:38 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
#include "nodes/pg_list.h"
#include "nodes/nodes.h"
#include "nodes/relation.h"
#include "utils/elog.h"

#include "optimizer/internal.h"
#include "optimizer/keys.h"
#include "optimizer/tlist.h"


static Expr *matching2_tlvar(int var, List *tlist, bool (*test)());

/*    
 * 1. index key
 * 	one of:
 * 		attnum
 * 		(attnum arrayindex)
 * 2. path key
 * 	(subkey1 ... subkeyN)
 * 	where subkeyI is a var node
 *    	note that the 'Keys field is a list of these
 * 3. join key
 * 	(outer-subkey inner-subkey)
 * 		where each subkey is a var node
 * 4. sort key
 * 	one of:
 * 		SortKey node
 * 		number
 * 		nil
 * 	(may also refer to the 'SortKey field of a SortKey node,
 * 	 which looks exactly like an index key)
 *    
 */

/*    
 * match-indexkey-operand--
 *    Returns t iff an index key 'index-key' matches the given clause 
 *    operand.
 *    
 */
bool
match_indexkey_operand(int indexkey, Var *operand, Rel *rel)
{
    if (IsA (operand,Var) &&
	(lfirsti(rel->relids) == operand->varno) &&
	equal_indexkey_var(indexkey,operand))
	return(true);
    else
	return(false);
}

/*    
 * equal_indexkey_var--
 *    Returns t iff an index key 'index-key' matches the corresponding 
 *    fields of var node 'var'.
 *    
 */
bool
equal_indexkey_var(int index_key, Var *var)
{
    if (index_key == var->varattno)
	return(true);
    else
	return(false);
}

/*    
 * extract-subkey--
 *   Returns the subkey in a join key corresponding to the outer or inner
 *   lelation.
 *    
 */
Var *
extract_subkey(JoinKey *jk, int which_subkey)
{
    Var *retval;

    switch (which_subkey) {
    case OUTER: 
	retval = jk->outer;
	break;
    case INNER: 
	retval = jk->inner;
	break;
    default:			/* do nothing */
	elog(DEBUG,"extract_subkey with neither INNER or OUTER");
	retval = NULL;
    }
    return(retval);
}

/*    
 * samekeys--
 *    Returns t iff two sets of path keys are equivalent.  They are 
 *    equivalent if the first subkey (var node) within each sublist of 
 *    list 'keys1' is contained within the corresponding sublist of 'keys2'.
 *    
 *    XXX 	It isn't necessary to check that each sublist exactly contain 
 *    		the same elements because if the routine that built these
 *    		sublists together is correct, having one element in common 
 *    		implies having all elements in common.
 *    
 */
bool
samekeys(List *keys1, List *keys2)
{
    bool allmember = true;
    List *key1, *key2;

    for(key1=keys1,key2=keys2 ; key1 != NIL && key2 !=NIL ; 
	key1=lnext(key1), key2=lnext(key2)) 
	if (!member(lfirst(key1), lfirst(key2)))
	    allmember = false;

    if ( (length (keys2) >= length (keys1)) && allmember)
	return(true);
    else
	return(false);
}

/*    
 * collect-index-pathkeys--
 *    Creates a list of subkeys by retrieving var nodes corresponding to
 *    each index key in 'index-keys' from the relation's target list
 *    'tlist'.  If the key is not in the target list, the key is irrelevant
 *    and is thrown away.  The returned subkey list is of the form:
 *    		((var1) (var2) ... (varn))
 *    
 * 'index-keys' is a list of index keys
 * 'tlist' is a relation target list
 *    
 * Returns the list of cons'd subkeys.
 *    
 */
/* This function is identical to matching_tlvar and tlistentry_member.
 * They should be merged.
 */
static Expr *
matching2_tlvar(int var, List *tlist, bool (*test)())
{
    TargetEntry *tlentry = NULL;

    if (var) {
	List *temp;
	foreach (temp,tlist) {
	    if ((*test)(var, get_expr(lfirst(temp)))) {
		tlentry = lfirst(temp);
		break;
	    }
	}
    }

    if (tlentry) 
	return((Expr*)get_expr(tlentry));
    else
	return((Expr*)NULL);
}


List *
collect_index_pathkeys(int *index_keys, List *tlist)
{
    List *retval = NIL;

    Assert (index_keys != NULL);

    while(index_keys[0] != 0) {
	Expr *mvar;
	mvar = matching2_tlvar(index_keys[0],
			       tlist,
			       equal_indexkey_var);
	if (mvar) 
	    retval = nconc(retval,lcons(lcons(mvar,NIL),
					NIL));
	index_keys++;
    }
    return(retval);
}

